This is a continuation-in-part of prior application Ser. No. 11/174,687, filed Jul. 5, 2005, which is hereby incorporated herein by reference in its entirety.
The present invention relates generally to so-called washpipe seals and more particularly, to a washpipe seal which is adapted to permit controlled leakage of a small portion of high pressure drilling fluid which largely passes into the so-called washpipe and into the drill string which is attached thereto. In the oil field industry particularly, a so-called swivel assembly incorporates a seal at the washpipe to confine the major portion of the drilling fluid to the washpipe. This drilling fluid is sometimes colloquially referred to as “drilling mud” or simply “mud.”
In the drilling system, there are high pressure abrasive fluids which are sent down to the bore hole through the washpipe and the drill string, and ultimately to the drill motor which is held at the bottom of the drill string. This abrasive fluid is supplied to the motor which drives the cutting tools under very high pressure, e.g. 5,000 PSI to 7,500 PSI or even 10,000 PSI or more. A seal is necessary between the non-rotary upper connection assembly and the rotary lower connection assembly to prevent undue leakage of this drilling fluid to the outside. As a rule, the drilling fluid leakage is taken from the vicinity of the washpipe back to a remote container where it is again picked up and supplied to the drill string. The joint in question is between the upper connection assembly, which includes a housing for the stator assembly and the lower connection assembly which includes the rotor assembly and which is affixed to and rotates with the drill string. The rotor and housing are sometimes collectively referred to as a “cartridge.”
According to one embodiment of the invention, the leakage of the drilling fluid, which is operated from 5,000 PSI up to perhaps 10,000 PSI or more for example, is led through a labyrinth between alternating rotor/stator discs, which preferably include lands and grooves in each rotor/stator disc. As the flow moves along between each rotor/stator it moves a radial distance about equal to the radial extent of each stator and rotor and an axial distance approximately equal to the thickness of each rotor and stator unit.
As a consequence of passing through this labyrinth of discs, the drilling fluid in one embodiment gradually is subject to a reduced pressure and ultimately achieves a low pressure and passes to an outlet, where it is led via a conduit back to the source of drilling fluid. Here, the drilling fluid passes back into the washpipe and undergoes a repetition of the cycle. According to the invention, only a very small portion of the drilling fluid escapes through the labyrinth seal compared to the portion of drilling fluid directed down the drill string, and the seal of the invention may thus be considered a controlled leakage seal.
In another embodiment, the force of the controlled leakage drilling fluid is opposed by grease within the labyrinth, whereby the grease fills most or all of the labyrinth and is present at what, in another embodiment, would be the inlet for the drilling fluid. The grease thus passes backwardly through the labyrinth of rotors and stators up to the approximate point of entry of the drilling fluid. In this embodiment, the drilling fluid is sealed at the top rather than at the bottom of the labyrinth, and the grease extends back and totally fills the labyrinth defined by the rotors and stators.
In either of these embodiments, it is possible and in fact probable that the cartridge, comprising the housing, or the fixed portion of the cartridges, the rotor and its included portions will need to be replaced or serviced, often fairly frequently, during the continuation of their operation. In the past the manner in which the fixed housing and the rotor have been hooked up is such that, in order to maintain it or replace parts, the system would have to be disabled, and the parts taken apart by unscrewing them on one or both sides. Thereafter, removing them would be extremely difficult because of the structure surrounding the washpipe unit. In other words, a structure that could permit the ready removal of the housing and rotor, sometimes collectively called the cartridge, and permit replacement of them with very little or no difficulty, would be highly desirable. This is done by providing a master coupling with at least one opening and preferably by attaching the cartridges with flanges which are clamped together and easily taken apart.
One of the features of the present invention is that the stator discs and the rotor discs are interleaved and arranged with very small clearance spaces between them. Consequently, in the stator unit there are a plurality of spacers, with a stator disc between each set of spacers. Also, there are a plurality of rotors, each one in turn separated by spacers. Consequently, there is an alternating stack of interleaved rotors and spacers which maintain the desired clearance. Each disc, in one embodiment, has a plurality of grooves of perhaps 0.005 to 0.050 inches, as well as a large plurality of lands which extend into the grooves, perhaps 0.005 to 0.040 inches by way of example. Each of the stator spacers and the rotor spacers is preferably held snugly in the desired configuration of a stack by Belleville washers or other similar units, and each of the spacers includes an O-ring or similar packing to ensure the correct alignment and spacing and to insure that there is no leakage through a secondary route. Thus, the spacers are held snugly in place by Belleville washer and the o-rings under compression. In addition, the rotor disks and the stators are held onto the inner and outer housings by keyways having locking pins associated with them, as will appear.
At the top of one embodiment of the novel rotor/stator assembly of the invention, is an annular space between sections of the housing and above the labyrinth. The drilling fluid pressure at this point is perhaps 5,000 to 10,000 PSI, but by reason of passing through the extended labyrinth with perhaps 16 to 20 reversals of radial direction and 16 to 20 axial movements as the drilling fluid moves along a tortuous path, the pressure confining the axial fluid gradually lowers until the fluid reaches the outlet, where it is under relatively low pressure and relatively low flow.
In one preferred embodiment, there is a flow meter in series relation with the drilling fluid escaping from the outlet. In this way, if there is an unexpected or sudden increase in flow, indicative of failure, steps may be taken to promptly rectify any malfunction.
In one embodiment of the prior art, there have been a series of seals, each seeing the highest pressure, and these seals would then fail, one at a time, until there remained only the final seal. This solution was not satisfactory, especially because of a projected seal life of only 50 to 300 hours. The present invention overcomes the difficulties with such seal designs by allowing the pressure to gradually bleed off rather than completely fail in a series of steps, each of which would see all of the pressure.
Because the fluid to be sealed is highly abrasive, the washpipe and the housing are preferably made from an oil field grade of steel and the rotor and stator its associated parts are made from tungsten carbide or other wear-resistant alloys, or other materials with wear-resistant coatings which are also used to provide radial and thrust bearings where the washpipe meets the upper housing. Such parts could also be made from ceramics or other like material. These bushings or bearings are greased through one or more fittings and grease passages which are provided for that purpose.
A known type of seal or packing is used between the lowermost portion of the washpipe and the stator and rotor housings, but this seal or packing sees only the reduced or lowermost pressure which is sensed at the outlet for the drilling fluid and accordingly, such seal is not exposed to high pressure in use.
It is therefore an object of the present invention to provide a new and improved seal for washpipes and similar applications, in oil fields and elsewhere.
A further object of the invention is to provide a washpipe seal wherein the high pressure drilling fluid moves gradually from a region of very high pressure, to a low outlet pressure from where it preferably is returned to the storage point for reuse.
Another object is to provide a seal which includes a housing for a plurality of stators and a housing for a plurality of rotors, with the stators and rotors being of annular disc form and being interleaved with one another.
A still further object of the invention is to provide a plurality of stators and rotors having interleaved portions and wherein each stator and rotor preferably includes a plurality of lands and grooves or other formations to retard the flow of drilling fluid as it works it way from the inlet chamber of the seal assembly to the outlet at the bottom portion thereof.
A still further object of the invention is to provide a plurality of alternating rotors and stators of annular form in which each includes a seal or packing that prevents leakage between the two sets of stators and rotors.
Another object of the invention is to provide a seal with a housing having a lower end member disposed in opposed relation to another housing member, the two being separated by thrust bearings and/or radial bearings each able to be greased, and maintaining such respective housings in closely spaced apart relation.
A further object is to provide a plurality of stators and rotors, each of which is held in place by a spacer, with the array of spacers being held in fixed position under a compressive load provided by spring means such as Belleville washers, for example.
Another object is to provide a construction wherein the stators are located for anti-rotation and the rotors are located for rotation by means of keyways and locking pins positioned on the outside diameter of the stator disks and the inside diameter of the rotor disks. Belleville washers are used to provide a small preload to the rotor and stator stack and the clamping of the total assembly compresses the stator and rotor spacers to fix the final position, while also providing an adequate seal between the components.
Another object of the invention is to provide radially inner and outer housings, each having a plurality of associated discs, with the inner housing including disks of annular form and defining a cylindrical region on the interior, able to accommodate a high volume of drilling fluid, while passing a small amount of drilling fluid to the annular headspace or chamber between the two housings.
A still further object of the invention is to provide a seal with controlled leakage, which includes an upper connection assembly and a housing attached thereto as well as a lower connection assembly that rotates with the washpipe in the use of the seal assembly.
A further object of the invention is to provide a washpipe seal which may be readily removed and replaced without altering the axial distance between the two connectors, that is, those at the top and the bottom of the assembly.
A still further object of the invention is to provide a system which will hold two parts of the wash pipe seal in snug, non-leaking relation but which can be readily radially removed so that the cartridge can be taken out of the system and replaced with another cartridge, with very little or no difficulty, and no changing of the ultimate distance between the upper and lower pipe flanges or connectors.
Another object is to provide a pair of clamps which can be separated by removing two fasteners on each end and removing the clamps, thereby enabling the cartridge to be removed radially and replaced with very little difficulty.
A still further object is to provide a pair of clamps which act radially and not only permit ease of removal, but also provide inherent alignment and clamping forces which prevent any possible leakage when the clamps are secured.